Strangeness in GiBUU · Manley: PWA including ˇN !ˇN and ˇN !2ˇN data no strangeness data included no strangeness via explicit resonance production Manley assigns some K decay

Strangeness in GiBUU

Janus Weil

FIAS

Strangeness WorkshopHeidelberg, 21. July 2014

Janus Weil Strangeness in GiBUU

Outline

the GiBUU model

particle production at SIS energies

strange & non-strange, resonances

Kaon potential

comparison to HADES pp / pNb at 3.5 GeV

current & future developments


The GiBUU model

hadronic transport model (microscopic, non-equilibrium),based on the BUU equation

developed for 20+ years in Giessen (in the group of U. Mosel)

current contributors: T. Gaitanos, K. Gallmeister, A.Larionov, J. Weil, U. Mosel

unified framework for electroweak (γA, eA, νA) and hadronic(pA, πA, AA) nuclear reactions

rather modern Fortran95 code base (∼ 200.000 LOC)publicly available releases (open source)

O. Buss et al., Phys. Rep. 512 (2012), http://gibuu.hepforge.org


The BUU equation

BUU equ.: space-time evolution of phase-space density F(via gradient expansion from Kadanoff-Baym)

∂(p0−H)∂pµ

∂F (x ,p)∂xµ −

∂(p0−H)∂xµ

∂F (x ,p)∂pµ = C (x , p)

degrees of freedom: hadrons(61 baryons and 22 mesons included)

Hamiltonian H:

hadronic mean fields (Skyrme or RMF), Coulomb, ...

collision term C (x , p): decays and collisions

low energy: resonance-model approachhigh energy: string fragment. (Pythia)

solve numerically via test-particle method:

F =∑i

δ(~r −~ri )δ(p − pi )


Particle Production at SIS:Resonances vs Strings

string theshold for mB:√s = 2.2± 0.2GeV ≈ mmaxR

(rougly corresponds to heaviest resonances)

for BB:√s = 3.4± 0.1GeV,

between mN + mmaxR ≈ 3.1GeV and 2mmaxR ≈ 4.4GeV


strange vs. non-strange sector

non-strange:

1 resonance production: NN → NR,∆R2 subsequent resonance decay: R → πN, ηN, ρN, σN, π∆, πN∗

(no strange decays here)3 possibly: dilepton decays

strangeness:

1 direct 3-body production: NN → BYK(B = N,∆, Y = Λ,Σ, K = K+,K 0)

2 cross sections parametrized by Tsushima et al.3 based on R prod. and decay, but in the end: just a

parametrization

somewhat inconsistent (explicit two-step production fornon-strange mesons, but direct 3-body production for Kaons)

but: no ’overlap’, both sectors are completely separated


non-strange Resonance Model

assumption: inel. NN cross section is dominated byproduction and decay of baryonic resonances

NN → NR,∆R (R : ∆, 7 N∗ and 6 ∆∗ states)based on Teis RM [Z. Phys. A 356, 1997] with several extensions

all π, η and ρ mesons produced via R decays (ω, φ: non-res.)

good descr. of total NN cross sections up to√s ≈ 3.5GeV

0

5

10

15

20

25

30

35

40

2 2.5 3 3.5 4

σin

el [

mb

]

sqrt(s) [GeV]

pp → X

SIS

2 2.5 3 3.5 4 0

5

10

15

20

25

30

35

40

sqrt(s) [GeV]

np → X

datainel.N∆

NN*N∆*∆∆

∆N*∆∆*

NNπω/φ

BYK


Resonance Production

NN → N∆: OBE model [Dmitriev et al, NPA 459 (1986)]

other resonances produced via phase-space approach(constant matrix elements):

σNN→NR =CIpi s

|MNR |2

16π

∫dµAR(µ)pF (µ)

σNN→∆R =CIpi s

|M∆R |2

16π

∫dµ1dµ2A∆(µ1)AR(µ2)pF (µ1, µ2)

lately: introduced angular distributions dσ/dt = b/ta, a ≈ 1(Eur.Phys.J. A502014)


Resonance parameters

all resonance parameters & decays modes taken from:Manley/Saleski, Phys. Rev. D 45 (1992)

Manley: PWA including πN → πN and πN → 2πN datano strangeness data included

no strangeness via explicit resonance production

Manley assigns some ΛK decay channels, but thoseresonances are not produced in NN collisions


Strangeness: Tsushima model

Tsushima et al. calculated Kaon production via intermediateresonances in eff. Lagr. model (OBE), Phys. Rev. C59 (1999)

BB → BYK (B = N,∆, Y = Λ,Σ, K = K+,K 0)final results are parametrized as σ = a(s/s0 − 1)b(s/s0)c

we just use the parametrization!


HADES: pp → K 0SX @ 3.5 GeV

original model: Tsushima et al. (dashed)

modified to fit elem. HADES Kaon data (solid lines):

parameters had to be adjusted for some channels5-body channels added (pp → ∆Y ∗K → ππNYK )

arXiv:1404.7011

[MeV/c]t

p0 200 400 600 800

[nb/(

MeV

/c)]

t/d

pσ

d

0

5

10

15

20 < -0.45CM-0.65 < y

[MeV/c]t

p0 200 400 600 800

[nb/(

MeV

/c)]

t/d

pσ

d

0

10

20

30 < -0.25CM

-0.45 < y

[MeV/c]t

p0 200 400 600 800

[nb/(

MeV

/c)]

t/d

pσ

d

0

10

20

30

40 < -0.05

CM-0.25 < y

[MeV/c]t

p0 200 400 600 800

[nb/(

MeV

/c)]

t/d

pσ

d

0

10

20

30

40 < 0.15

CM-0.05 < y

[MeV/c]t

p0 200 400 600 800

[nb/(

MeV

/c)]

t/d

pσ

d

0

10

20

30 < 0.35

CM0.15 < y

[MeV/c]t

p0 200 400 600 800

[nb/(

MeV

/c)]

t/d

pσ

d0

10

20

30

< 0.55CM

0.35 < y


Kaon Potential

ChPT kaon potential:

m∗K =√m2K −

ΣKNf 2πρs + VµV µ

Brown/Rho, NPA596, 1996Schaffner-Bielich, NPA625, 1997

includes density and momentumdependence (non-linear)

repulsive for K+,K 0

attractive for K−,K0

U = E ∗ − E ≈ 35 MeV for K+,K 0at ρ = ρ0, ~p = 0

]-3

[fmρ

0 0.05 0.1 0.15 0.2

p [

Ge

V/c

]

0

0.5

1

1.5

2

0

10

20

30

40

50

60

70MeV


secondary KN collisions

left: K+p; right: K−p

good agreement with data, many channels contributing


HADES: pNb→ K 0s X @ 3.5 GeV

rap. spectrum mostly insensitive to potential in measuredregion (left)

momentum spectra most sensitive in forward region (right)

take ratio of two polar-angle bins to get rid of systematicuncertainties in abs. norm. (arXiv:1404.7011)

��

��

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systematics well under control

good baseline from pp at same energy

limited density (ρ ≤ ρ0)Janus Weil Strangeness in GiBUU

Conclusions

HADES pNb data show indications of repulsive K 0 potential

consistent with ChPT potential of U(ρ0) = 35 MeV

cold nuclear matter setup has less systematic uncertaintiesthan heavy-ion collisions

(but: effects not quite as large)


announcement: GiBUU is open source!

GiBUU had ’public releases’ for some time, but they were onlyavailable after registration

since last week: GiBUU release 1.6 is fully public, can bedownloaded via anonymous svn checkout (w/o registr.)

https://gibuu.hepforge.org/trac/wiki/svn

development version continues to be private

next open release 1.7 later this year


The future: SMASH

next-generation transport code, currently being developed inthe group of Hannah Petersen at FIAS

core tream: H. Petersen, J. Auvinen, M. Kretz, J. Weil(+students)

aim: clean, modern and future-proof code, which takesadvantage of modern computing arch. (multicore,heterogenous), written from scratch in C++

current status: preparing internal version 0.4,∼20.000 lines of C++ codefirst public release by next year?


The End

Thanks for your attention!


Documents

Strangeness in GiBUU · Manley: PWA including ˇN !ˇN and ˇN !2ˇN data no strangeness data included no strangeness via explicit resonance production Manley assigns some K decay